This patent application claims priority to and all advantages of German Application No. 10029803.6, entitled xe2x80x9cClearcoat Material And Its Use To Produce Clearcoats And Multicoat Color And/Or Effect Coating Systems,xe2x80x9d which was filed on Jun. 16, 2000.
The subject invention generally relates to a curable, water-based coating composition utilized primarily in waterborne coating systems, such as waterborne basecoat (WBBC) systems, waterborne clearcoat (WBCC) systems, and waterborne primer systems. More specifically, the coating composition includes a water-based copolymer, having a carbonate functional group, and a cross-linking agent including an amino functional group that is reactive with the carbonate functional group. The subject invention also relates to a method of preparing the coating composition as well as a method of preparing a cured film of the coating composition.
Water-based coating compositions include water-based copolymers and cross-linking agents as components. The water-based copolymers are desirable for use in coating systems in the automotive and industrial coatings industries because these copolymers enable formulation of waterborne coating systems, such as WBBC, WBCC, and waterborne primer systems. It is known in the art that waterborne coating systems are ideal as compared to solventborne coating systems because waterborne coating systems have lower content of volatile organic compounds (VOCs).
The water-based copolymers of the prior art have proven to be inadequate for use as a component in water-based coating compositions. The water-based copolymers of the prior art are ineffective because these copolymers are highly viscous, as secondary dispersions, and generally have poorly defined film forming characteristics, as primary dispersions. Furthermore, the cross-linking between these copolymers and such conventional cross-linking agents, such as aminoplasts, are often particularly susceptible to environmental acid etch.
The water-based copolymers of the prior art are also deficient because these copolymers often incorporate additional components such as co-solvents and surfactants which are both undesirable components in waterborne coating systems. For instance, conventional water-based copolymers typically incorporate a co-solvent to promote dispersibility of the copolymer in water, and these co-solvents contribute to increased VOCs. Conventional water-based copolymers also typically incorporate surfactants to promote and maintain miscibility and incorporation of the copolymer in water, and as understood by those skilled in the art, the incorporation of surfactants into coating compositions frequently contributes to water sensitivity, humidity, and xe2x80x98crateringxe2x80x99 as well as other coating defects detrimental to the appearance of the waterborne coating system.
The free-radical polymerization methods of preparing the water-based copolymers of the prior art are also deficient. These conventional methods are typically highly exothermic and are therefore difficult to predict and control. The unpredictability of these methods leads to uncontrollable and inconsistent physical properties of the water-based copolymer and ultimately of the water-based coating composition which includes the copolymer as a component. More specifically, the unpredictability of these methods frequently leads to inconsistent molecular weight distribution of the copolymer, and to incomplete conversion of monomer components into the copolymer. Furthermore, in the preparation of conventional water-based copolymers, distribution of the monomer components is random and does not produce a xe2x80x98tailoredxe2x80x99 polymeric architecture that is able to meet particular needs depending on whether the copolymer is utilized in a WBBC, WBCC, or waterborne primer system. It is understood in the art that inconsistent molecular weights, incomplete conversion of monomer components, and even random distribution of the monomer components affects, among other things, the stability of the viscosity of the copolymer and can even result in xe2x80x98gellingxe2x80x99 of the copolymer and of the water-based coating composition. Additionally, poor appearance characteristics of the WBBC, WBCC, or waterborne primer system, such as gloss and distinctness of image (DOI), can result from poor rheology, i.e., flow, of the coating composition upon application that is due to the inconsistencies in the water-based copolymer.
In sum, the prior art water-based copolymers which are components of the water-based coating composition, as detailed above, are characterized by one or more inadequacies. Due to the inadequacies identified in the prior art, it is desirable to provide a novel water-based copolymer and coating composition to be utilized in WBBC, WBCC, and waterborne primer systems as well as a novel method of preparing the coating composition and a cured film.
A curable, water-based coating composition is disclosed. The water-based coating composition of the subject invention is the reaction product of a water-based copolymer (A) and at least one cross-linking agent (B). The water-based copolymer (A) is prepared by free-radical polymerization and includes a first block polymer, or first block, (A)(I) and a second block (A)(II). The first block (A)(I) is preferably a hydrophilic block, and the second block (A)(II) is preferably a hydrophobic block. More specifically, the first block (A)(I) of the copolymer (A) is the reaction product of at least one ethylenically unsaturated monomer (A)(I)(a), and at least one vinylaromatic hydrocarbon monomer (A)(I)(b). The second block (A)(II) of the copolymer (A) is the reaction product of a plurality of ethylenically unsaturated monomers (A)(II)(a) different than the ethylenically unsaturated monomer (A)(I)(a), wherein at least one of the plurality (A)(II)(a) includes at least one carbonate functional group. The cross-linking agent (B) is reactive with the carbonate functional group and is selected from the group consisting of water-soluble, C2 to C20 alkyl compounds having at least one amino functional group.
In the preferred water-based coating composition of the subject invention, the at least one ethylenically unsaturated monomer (A)(I)(a) of the first block (A)(I) is further defined as a first and second ethylenically unsaturated monomer where the first ethylenically unsaturated monomer is preferably acrylic acid, and the second ethylenically unsaturated monomer is preferably methyl methacrylate. Furthermore, the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) of the first block (A)(I) is preferably diphenylethylene. Also in the preferred embodiment, the plurality of ethylenically unsaturated monomers (A)(II)(a) of the second block (A)(II) that are different than the at least one ethylenically unsaturated monomer (A)(I)(a) are styrene, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and carbonate-modified glycidyl methacrylate having the carbonate functional group. Finally, the preferred cross-linking agent (B) that is reactive with the carbonate functional group is triaminononane.
A method of preparing the water-based coating composition is also disclosed. According to this method, the first block (A)(I) is first formed. Next, the second block (A)(II), having the at least one carbonate functional group, is polymerized with the first block (A)(I) to establish the water-based copolymer (A). The copolymer (A) is then combined with the cross-linking agent (B) such that the amino functional group of the cross-linking agent (B) is reactive with the carbonate functional group thereby forming the water-based coating composition of the subject invention.
The general object of the subject invention is to develop a water-based coating composition for use in WBBC, WBCC, and waterborne primer systems that utilizes carbonatexe2x80x94amine cross-linking through a water-based copolymer (A), having a carbonate functional group, and a cross-linking agent (B) including an amino functional group that is reactive with the carbonate functional group. It is also a general object to introduce a water-based coating composition that is completely solvent-free, i.e., does not utilize any co-solvents, such that the content of VOCs is zero while maintaining the dispersibility of the copolymer (A) in water without any co-solvents.
It is a further object of the subject invention to develop a water-based coating composition that includes a lower cost cross-linking agent (B) reactive with the carbonate functional group such that the WBBC, WBCC, and waterborne primer systems prepared from the water-based coating composition of the subject invention are resistant to environmental acid etch. It is a further object of the subject invention to develop a water-based coating composition that is surfactant-free, yet still fully miscible in water, such that the WBBC, WBBC, and waterborne primer systems prepared from the water-based coating composition of the subject invention are crater resistant and do not suffer from other surfactant-related defects.
Regarding the method of preparing the water-based coating composition, it is an object of the subject invention to introduce a novel method that thoroughly converts monomer components into the copolymer (A) and that is predictable and controllable such that the structure of the copolymer (A) can be xe2x80x98tailoredxe2x80x99 and achieved. Therefore, water-based coating compositions prepared according to the method of the subject invention maintain stable viscosities and result in cured films in either a WBBC, a WBCC, or a waterborne primer system having ideal appearance characteristics.
The curable, water-based coating composition of the subject invention is utilized in waterborne coating systems. Waterborne coating systems, such as waterborne basecoat (WBBC) systems and waterborne clearcoat (WBCC) systems, are used throughout automotive, industrial, and other coatings industries to coat various substrates for aesthetic and functional purposes, such as color and environmental resistance, respectively. Although the subject invention is directed at WBBC and WBCC systems, it is to be understood that the subject invention may also be utilized in other waterborne coating systems including, but not limited to waterborne primer systems, and in other industries including, but not limited to, the adhesive and sealant industries.
The water-based coating composition of the subject invention includes the reaction product of a water-based copolymer (A), having at least one carbonate functional group, and of at least one cross-linking agent (B) including at least one amino, NH2, functional group. As will be described further below, the amino functional group of the cross-linking agent (B) reacts with the carbonate functional group to establish urethane (xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94) cross-linking without use of an isocyanate. The water-based coating composition is prepared by a free-radical polymerization method. In general, the method of preparing the coating composition includes the steps of forming a first block (A)(I), polymerizing a second block (A)(II) with the first block (A)(I) to establish the water-based copolymer (A), and combining the water-based copolymer (A) with the cross-linking agent (B) to form the water-based coating composition of the subject invention with urethane cross-linking from the carbonatexe2x80x94amine reaction. These method steps will be discussed in greater detail below.
The water-based copolymer (A) is the reaction product of the first block (A)(I) and the second block (A)(II). In the most preferred embodiment, the first block (A)(I) is a hydrophilic block, and the second block (A)(II) is a hydrophobic block, and the subject invention will be described with this in mind. However, it is to be understood that the number of blocks, as described two blocks, is not intended to be limiting. For instance, the water-based copolymer (A) could also be the reaction product of three blocks, e.g. a first hydrophilic block, a second hydrophilic block, and a first hydrophobic block.
The first block (A)(I) is present in an amount from 5 to 15, preferably from 7 to 10, parts by weight based on 100 parts by weight of the coating composition. The first block (A)(I) is the reaction product of at least one ethylenically unsaturated monomer (A)(I)(a) and of at least one vinylaromatic hydrocarbon monomer (A)(I)(b). More specifically, to form the first block (A)(I), the at least one ethylenically unsaturated monomer (A)(I)(a) and at least one vinylaromatic hydrocarbon monomer (A)(I)(b) are polymerized. This polymerization step is conducted over time from 1 to 8, preferably from 2 to 7, and most preferably from 4 to 6, hours, and at a temperature between 50xc2x0 C. and 100xc2x0 C. It is to be understood that the time required to conduct this xe2x80x98polymerization stepxe2x80x99 includes the time needed for the addition of monomer components as well as any holding or cooling time, where the addition of monomers may not be occurring. It is also to be understood that certain ethylenically unsaturated monomers (A)(I)(a) and certain vinylaromatic hydrocarbon monomers (A)(I)(b) require that the polymerization step be conducted under pressure. If required, such pressure is preferably from 1.5 to 3000 bar, and more preferably from 10 to 1000 bar.
The at least one ethylenically unsaturated monomer (A)(I)(a) of the first block (A)(I) is selected primarily to ensure the solubility of the copolymer (A) in water. As such, the at least one ethylenically unsaturated monomer (A)(I)(a) is selected to form a salt when reacted with a neutralizing agent. The neutralizing agent will be discussed further below. In addition to the primary purpose of ensuring the solubility of the copolymer (A) in water, the at least one ethylenically unsaturated monomer (A)(I)(a) may also be selected to achieve an ideal minimum film forming temperature, MFFT, for the water-based copolymer (A), and ultimately for a cured film of the water-based coating composition utilized in either the WBBC, WBCC, or waterborne primer system, such that the cured film is resistant to excessive cracking, chipping, and the like. The at least one ethylenically unsaturated monomer (A)(I)(a) may also be selected to minimize the photo-sensitivity of the coating composition and of the cured film formed of the coating composition.
In the preferred embodiment of the subject invention, the at least one ethylenically unsaturated monomer (A)(I)(a) is further defined as a first and second ethylenically unsaturated monomer. The first and second ethylenically unsaturated monomers are selected in order to balance the desired physical characteristics as discussed above. That is, the first and second ethylenically unsaturated monomers are selected to balance the solubility of the copolymer (A) in water as well as the MFFT and the photosensitivity of the coating composition and of the cured film. In terms of the total monomer composition in the first block (A)(I) of the copolymer (A), the first and second ethylenically unsaturated monomers form from 70 to 99, preferably from 90 to 96, parts by weight based on 100 parts by weight of total monomer composition in the first block (A)(I). It is to be understood that, in addition to the content of the first and second ethylenically unsaturated monomers, the total monomer composition in the first block (A)(I) also includes the content of the at least one vinylaromatic hydrocarbon monomer (A)(I)(b). As will be discussed in greater detail below, in certain embodiments, the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) is alternatively defined as at least one ethylenically unsaturated monomer (A)(I)(b) that is different than the at least one ethylenically unsaturated monomer (A)(I)(a) and of the general formula R1R2C=CR3R4. In such embodiments, the total monomer composition in the first block (A)(I) is defined to include the content of the at least one ethylenically unsaturated monomer (A)(I)(b) of the general formula R1R2C=CR3R4. In the preferred embodiment, the weight ratio of the first ethylenically unsaturated monomer to the second ethylenically unsaturated monomer in the first block (A)(I) is from 1:0.5 to 1:5.
The first ethylenically unsaturated monomer is selected from the group of compounds consisting of alkyl acrylic acids. The second ethylenically unsaturated monomer is selected from the group of compounds consisting of aliphatic acrylates, aliphatic methacrylates, cycloaliphatic acrylates, cycloaliphatic methacrylates, and mixtures thereof of each of these compounds. It is to be understood that each of these compounds include an alkyl radical, and in the preferred embodiment of the subject invention, each of these compounds includes up to 20 carbon atoms in the alkyl radical.
The alkyl acrylic acids that may be selected as the first ethylenically unsaturated monomer are selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and mixtures thereof. The aliphatic acrylates that may be selected as the second ethylenically unsaturated monomer are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, and mixtures thereof. The aliphatic methacrylates that may be selected as the second ethylenically unsaturated monomer are selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, and mixtures thereof. The cycloaliphatic acrylate that may be selected as the second ethylenically unsaturated monomer is cyclohexyl acrylate, and the cycloaliphatic methacrylate that may be selected as the second ethylenically unsaturated monomer is cyclohexyl methacrylate.
In the most preferred embodiment of the subject invention, the first ethylenically unsaturated monomer is acrylic acid, and the second ethylenically unsaturated monomer is methyl methacrylate. Furthermore, the weight ratio of the acrylic acid to the methyl methacrylate in the first block (A)(I) is from 1:0.5 to 1:3 in the most preferred embodiment.
The at least one vinylaromatic hydrocarbon monomer (A)(I)(b) of the first block (A)(I) is selected from the group consisting of xcex1-methylstyrene, diphenylethylene, dinapthaleneethylene, and mixtures thereof. Further, it is to be understood that other xcex1-alkylstyrenes may be selected as the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) as well as other equivalent compounds including, but not limited to, cis- or trans-stilbene, vinylidenebis (4-N,N-dimethylaminobenzene), vinylidenebis (4-aminobenzene), or vinylidenebis (4-nitrobenzene). Although more than one vinylaromatic hydrocarbon monomer (A)(I)(b) may be included in the first block (A)(I), the preferred embodiment of the subject invention includes only one vinylaromatic hydrocarbon monomer, most preferably diphenylethylene. In terms of the total monomer composition in the first block (A)(I) of the copolymer (A), the vinylaromatic hydrocarbon monomer forms from 1 to 20, preferably from 3 to 7, parts by weight based on 100 parts by weight of total monomer composition in the first block (A)(I).
In certain embodiments, the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) of the first block (A)(I) may alternatively be defined as the at least one ethylenically unsaturated monomer (A)(I)(b) that is different than the at least one ethylenically unsaturated monomer (A)(I)(a) and that is of the general formula 
In these embodiments, the radicals R1, R2, R3, and R4, each independently of one another are hydrogen atoms or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl or arylcycloalkyl radicals, with the proviso that at least two of the variables R1, R2, R3, and R4 are substituted or unsubstituted aryl, arylalkyl or arylcycloalkyl radicals, especially substituted or unsubstituted aryl radicals.
Examples of suitable alkyl radicals are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, amyl, hexyl, or 2-ethylhexyl.
Examples of suitable cycloalkyl radicals are cyclobutyl, cyclopentyl, or cyclohexyl.
Examples of suitable alkylcycloalkyl radicals are methylenecyclohexane, ethylenecyclohexane, or propane 1,3-diylcyclohexane.
Examples of suitable cycloalkylalkyl radicals are 2-, 3-, or 4-methyl-, -ethyl-, -propyl-, or -butylcyclohex-1-yl.
Examples of suitable aryl radicals are phenyl, naphthyl or biphenylyl, preferably phenyl and naphthyl, and especially phenyl.
Examples of suitable alkylaryl radicals are benzyl or ethylene- or propane-1,3-diylbenzene.
Examples of suitable cycloalkylaryl radicals are 2-, 3-, or 4-phenylcyclohex-1-yl.
Examples of suitable arylalkyl radicals are 2-, 3-, or 4-methyl-, -ethyl-, -propyl-, or -butylphen-1-yl.
Examples of suitable arylcycloalkyl radicals are 2-, 3-, or 4-cyclohexylphen-1-yl.
The above-described radicals R1, R2, R3, and R4 may be substituted. The substituents used may comprise electron-withdrawing or electron-donating atoms or organic radicals. Examples of suitable substituents are halogen atoms, especially chlorine and fluorine, nitrile groups, nitro groups, partially or fully halogenated, especially chlorinated and/or fluorinated, alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl and arylcycloalkyl radicals, including those exemplified above, especially tert-butyl; aryloxy, alkyloxy and cycloalkyloxy radicals, especially phenoxy, naphthoxy, methoxy, ethoxy, propoxy, butyloxy or cyclohexyloxy; arylthio, alkylthio and cycloalkylthio radicals, especially phenylthio, naphthylthio, methylthio, ethylthio, propylthio, butylthio or cyclohexylthio; hydroxyl groups; and/or primary, secondary and/or tertiary amino groups, especially amino, N-methylamino, N-ethylamino, N-propylamino, N-phenylamino, N-cyclohexylamino, N,N-dimethylamino, N,N-diethylamino, N,N-dipropylamino, N,N-diphenylamino, N,N,-dicyclohexylamino, N-cyclo-hexyl-N-methylamino and N-ethyl-N-methylamino.
Examples of ethylenically unsaturated monomers (A)(I)(b) whose use is particularly preferred in these embodiments are diphenylethylene, dinaphthaleneethylene, cis- or trans-stilbene, vinylidenebis (4-N,N-dimethylamino-benzene), vinylidenebis (4-aminobenzene), and vinylidenebis (4-nitrobenzene).
Also, in accordance with these embodiments, ethylenically unsaturated monomers (A)(I)(b) may be used individually or as a mixture of at least two monomers (A)(I)(b).
Finally, as with the preferred embodiment which includes the at least one vinylaromatic hydrocarbon monomer (A)(I)(b), the preferred ethylenically unsaturated monomers (A)(I)(b) in these alternative embodiments is diphenylethylene.
In addition to the at least one ethylenically unsaturated monomer (A)(I)(a) and the at least one vinylaromatic hydrocarbon monomer (A)(I)(b), the first block (A)(I) is also the reaction product of the neutralizing agent. That is, the neutralizing agent is added to the at least one ethylenically unsaturated monomer (A)(I)(a) and to the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) to form the first block (A)(I) of the water-based copolymer (A). Specifically, the neutralizing agent is selected from the group consisting of dimethylethanolamine, amino methyl propanol, ammonia, and mixtures thereof. It is to be understood that other base neutralizing agents may selected including, but not limited to, sodium hydroxide, potassium hydroxide, diethanolamine, triethanolamine, and mono-, di-, or tri-ethylamine. In the preferred embodiment, the neutralizing agent is ammonia, NH3. The ammonia, NH3, interacts with an acid group of the first ethylenically unsaturated monomer. More specifically, in the preferred embodiment, the ammonia, NH3, interacts with the hydrogen atom of the xe2x80x94COOH group of the acrylic acid, to form a salt of the acrylic acid, having a xe2x80x94COO group, i.e., an acid anion group, and NH4+. The salt of acrylic acid ensures the solubility of the copolymer (A) in water.
Like the neutralizing agent, an initiator, also known a polymerization promoter, is added to the at least one ethylenically unsaturated monomer (A)(I)(a) and to the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) to form the first block (A)(I) of the water-based copolymer (A). The initiator initiates the free-radical polymerization process. The initiator is soluble in water and is selected from the group consisting of inorganic persulfates, dialkyl peroxides, hydroperoxides, peresters, and mixtures thereof. In the preferred embodiment of the subject invention, the initiator is an inorganic persulfate selected from the group consisting of ammonium persulfate, (NH4)2S2O8, potassium persulfate, K2S2O8, and sodium persulfate, Na2S2O8. Most preferably, the initiator in ammonium persulfate. However, in alternative embodiments, the free-radical polymerization initiator may be a dialkyl peroxides such as di-tert-butyl peroxide or dicumyl peroxide, a hydroperoxide such as cumene hydroperoxide or tert-butyl hydroperoxide, or a perester, such as tert-butyl perbenzoate, tert-butyl perpivalate, tert-butyl per-3,4,5,-trimethylhexanoate or tert-butyl per-2-ethylhexanoate.
The weight ratio of the initiator to the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) is preferably from 1:3 to 3:1. It is to be understood that it is preferred to add comparatively large amounts of the initiator. More specifically, it is preferred that the initiator be present in an amount from 0.5 to 50, more preferably from 1.0 to 20, and most preferably from 3 to 10, parts by weight based on 100 parts by weight of total monomer composition in the first block (A)(I). At the completion of the formation of the first block (A)(I), the first block (A)(I) has a non-volatile content of from 20 to 50, preferably from 25 to 40, percent non-volatile by weight. Furthermore, the completed first block (A)(I) has a number average molecular weight, Mn, from 1,000 to 20,000, preferably from 3,000 to 10,000.
Next, monomers making up the second block (A)(II) having the at least one carbonate functional group, which will be described in detail below, are polymerized with the first block (A)(I) to establish the water-based copolymer (A). This polymerization step, between the monomers making up the second block (A)(II) and the first block (A)(I), is conducted over time from 1 to 8, preferably from 5 to 6, hours, and at a temperature between 50xc2x0 C. and 100xc2x0 C., more preferably between 80xc2x0 C. and 100xc2x0 C. As with the polymerization step for forming the first block (A)(I), it is to be understood that the time required to conduct this xe2x80x98polymerization stepxe2x80x99 includes the time needed for the addition of monomer components as well as any holding or cooling time, where the addition of monomers may not be occurring. Also, for this polymerization step, preferably no additional free-radical initiator is required. Instead, this polymerization step is preferably initiated by self-formation of radicals. Also, in this polymerization step, the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) of the first block (A)(I), in the preferred embodiment diphenylethylene, controls the polymerization of the incoming monomers that make up the second block (A)(II). The second block (A)(II) of the copolymer (A) is more specifically the reaction product of a plurality of ethylenically unsaturated monomers (A)(II)(a) that can be different than the ethylenically unsaturated monomer (A)(I)(a), and are present in an amount from 30 to 50, preferably from 35 to 45, parts by weight based on 100 parts by weight of the coating composition.
The plurality of ethylenically unsaturated monomers (A)(II)(a) are hydrophobic, i.e., insoluble in water, and in preparing the second block (A)(II) of the copolymer (A), the plurality of ethylenically unsaturated monomers (A)(II)(a) are selected to promote miscibility between the coating composition and other components commonly utilized in WBBC, WBCC, and waterborne primer systems. The plurality of ethylenically unsaturated monomers (A)(II)(a) are also selected to contribute to the MFFT for the water-based copolymer (A), and ultimately for the cured film of the water-based coating composition utilized in either the WBBC, WBCC, or waterborne primer systems.
At least one of the ethylenically unsaturated monomers of the plurality (A)(II)(a) includes at least one carbonate functional group. As such, the plurality of ethylenically unsaturated monomers (A)(II)(a) are selected from the group consisting of styrene, butyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, cyclohexyl methacrylate, glycidyl acrylate, glycidyl methacrylate, carbonate-modified glycidyl acrylate, carbonate-modified glycidyl methacrylate, and mixtures thereof, so long as the plurality of ethylenically unsaturated monomers (A)(II)(a) that are selected are different than the ethylenically unsaturated monomer (A)(I)(a). Also, as discussed above, at least one of the plurality (A)(II)(a) must introduce the carbonate functional group. Therefore, one of either carbonate-modified glycidyl acrylate or carbonate-modified glycidyl methacrylate is to be selected. Of course, it is understood that alternative carbonate-modified compounds can be introduced by other chemical compounds such as epoxy group containing compounds reacted with CO2, and even by chemical compounds having unsaturated bonds that are first converted to an epoxy group by known reactions with peroxides. As also understood by those skilled in the art, the carbonate-modified glycidyl acrylate is formed by the reaction of glycidyl acrylate, having the chemical formula of CH2:CHCOOCH2CHCH2O, with CO2, under excessive pressure and temperature conditions. Similarly, the carbonate-modified glycidyl methacrylate is formed by the reaction of glycidyl methacrylate, having the chemical formula of CH2:C(CH3)COOCH2CHCH2O, with CO2, under excessive pressure and temperature conditions. In the preferred embodiment, the plurality of ethylenically unsaturated monomers (A)(II)(a) that are selected are styrene, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and carbonate-modified glycidyl methacrylate which includes the carbonate functional group. For descriptive purposes, the common chemical name for carbonate-modified glycidyl methacrylate is 4-(hydroxymethyl)-1,3-dioxolan-2-one methacrylate and the accepted chemical abstract chemical name is 2-propenoic acid, 2-methyl-, (2-oxo-1,3-dioxalan-4-yl) methyl ester.
The water-based coating composition is also the reaction product of the at least one water-soluble cross-linking agent (B) including the at least one amino functional group, NH2, that is reactive with the carbonate functional group. In other words, the water-based copolymer (A) is combined with the cross-linking agent (B) to form the coating composition of the subject invention. Preferably, the cross-linking agent is a low cost, low molecular weight di-, tri-, or other poly-amine. More specifically, the at least one cross-linking agent is selected from the group consisting of water-soluble, C2 to C20 alkyl compounds that have at least one amino functional group including, but not limited to, hexamethylenediamine, triaminononane, and mixtures thereof. It is to be understood that water-soluble is intended to indicate that approximately 0.25 grams of cross-linking agent (B) or more can dissolve for every 100 ml of water. The preferred embodiment of the subject invention includes triaminononane, having three amino functional groups, as the only cross-linking agent (B). For descriptive purposes, triaminononane is the common chemical name, and 4-aminomethyl-1,8-octanediamine is the accepted chemical abstract chemical name. The cross-linking agent (B) is present in an amount from 1 to 10, preferably from 3 to 6, parts by weight based on 100 parts by weight of the coating composition.
Upon addition of the cross-linking agent (B) to the copolymer (A), the amino functional group of the cross-linking agent (B) reacts with the carbonate functional group. In terms of the preferred embodiment, the second block (A)(II) of the copolymer (A) includes carbonate-modified glycidyl methacrylate as a monomer component as disclosed in the following chemical representation. 
As shown schematically in the above chemical representation of the carbonate-modified glycidyl methacrylate of the preferred embodiment, the amino functional groups, NH2, of the triaminononane react at either (1) or (2) to open the ring and result either in a primary or secondary urethane (xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94) linkage. The resulting primary and secondary urethane linkages established in the coating composition of the subject invention are shown respectively in the following chemical representations. 
The resulting carbonatexe2x80x94amine cross-linking that establishes either urethane linkages shown above is ideal for resistance to environmental acid etch. Overall, the copolymer (A) has a number-average molecular weight, Mn, of from 5,000 to 2,000,000. Additionally, the coating composition of the subject invention has a non-volatile content of from 20 to 60, preferably from 30 to 50, percent non-volatile by weight, and an average volume particle size of xe2x89xa6200 nm.
The cured film of the water-based coating composition of the subject invention is prepared by applying the water-based coating composition to the substrate. More specifically, the water-based coating composition can be sprayed onto the substrate by air-atomized or bell-applied spray application, and other equivalent processes. Once applied to the substrate, the coating composition is cured to form the cured film. Although cross-linking may occur prior to the curing step, the at least one amino functional group of the cross-linking agent completely reacts with the at least one carbonate functional group during the curing step to form the cured film of the water-based coating composition including the urethane cross-linking. Preferably, the reaction between the amino functional group and the carbonate function group occurs at a temperature between 100xc2x0 C. and 175xc2x0 C., and more preferably at a temperature between 110xc2x0 C. and 130xc2x0 C. from 20 to 30 minutes.
It is to be understood that all of the preceding chemical representations are merely two-dimensional chemical representations and that the structure of these chemical representations may be other than as indicated.